Magnetic field sensor having sensing element placement for reducing stray field sensitivity

ABSTRACT

Methods and apparatus for a sensor having a first magnetic field sensing element with first and second segments where the first and second segments are located at positions of opposite magnetic field. The first and second segments are spaced from each other based upon iso-lines of the magnetic field. A processing module can process an output of the magnetic field sensing element.

BACKGROUND

Magnetic sensors are widely used in modern systems to measure or detectphysical parameters, such as magnetic field strength, current, position,motion, orientation, and so forth. There are many different types ofsensors for measuring magnetic fields and other parameters. However,such sensors suffer from various limitations, for example, excessivesize, inadequate sensitivity and/or dynamic range, cost, reliability andthe like. In addition, positional misalignment of a magnetic sensingelement can degrade sensor performance.

SUMMARY

The present invention provides method and apparatus for magnetic fieldsensors with magnetic field sensing elements and segments of a magneticfield sensor positioned with respect to a bias field of a magnet toreduce sensitivity to a common mode field. In embodiments, thedimensions and or spacing of elements and/or segments are configuredbased upon the magnetic bias field iso-lines. In embodiments, a magnetis shaped to make common mode field sensitivity of the magnetic fieldsensing elements substantially independent of element misplacement onthe die versus the magnet for a given axis for a range of misplacement.

In one aspect, a sensor comprises: a first magnetic field sensingelement comprising first and second segments wherein the first andsecond segments are located at positions of opposite magnetic field,wherein the first and second segments are spaced from each other basedupon iso-lines of the magnetic field; and a processing module to receivean output of the magnetic field sensing element.

A sensor can further include one or more of the following features: theiso-lines correspond to a bias field along an axis perpendicular to areference axis, the first and second segments are dimensioned to achievea substantially equal bias field distribution, a length of the firstand/or second segment is selected to equalize bias field distribution,the length and spacing of the first and second segments is selected toachieve a given zero field resistance, a second magnetic field sensingelement having third and fourth segments located at positions togenerate magnetic field bias in opposite directions for reducingsensitivity due to misalignment of the third and fourth segments, thefirst and second magnetic field sensing elements are configured inhalf-bridge configuration, third and fourth magnetic field sensingelements, wherein the first, second, third, and fourth magnetic fieldsensing elements are configured in a bridge configuration, the thirdmagnetic field sensing element comprises fifth and sixth segments andthe fourth magnetic field sensing element comprises seventh and eighthsegments, the first magnetic field sensing element comprises GMRelements, the first magnetic field sensing element comprises TMRelements, a shape of the magnet providing the bias field isnon-rectangular to decrease a slope of the bias field lines along agiven axis, the shape of the magnet is at least partially elliptical,the shape of the magnet is at least partially beveled, and/or the shapeof the magnetic is at least partially triangular.

In another aspect, a method comprises: employing a first magnetic fieldsensing element comprising first and second segments wherein the firstand second segments are located at positions of opposite magnetic field,wherein the first and second segments are spaced from each other basedupon iso-lines of the magnetic field; and employing a processing moduleto receive an output of the magnetic field sensing element.

A method can further include one or more of the following features: theiso-lines correspond to a bias field along an axis perpendicular to areference axis, the first and second segments are dimensioned to achievea substantially equal bias field distribution, a length of the firstand/or second segment is selected to equalize bias field distribution,the length and spacing of the first and second segments is selected toachieve a given zero field resistance, a second magnetic field sensingelement having third and fourth segments located at positions togenerate magnetic field bias in opposite directions for reducingsensitivity due to misalignment of the third and fourth segments, thefirst and second magnetic field sensing elements are configured inhalf-bridge configuration, third and fourth magnetic field sensingelements, wherein the first, second, third, and fourth magnetic fieldsensing elements are configured in a bridge configuration, the thirdmagnetic field sensing element comprises fifth and sixth segments andthe fourth magnetic field sensing element comprises seventh and eighthsegments, the first magnetic field sensing element comprises GMRelements, the first magnetic field sensing element comprises TMRelements, a shape of the magnet providing the bias field isnon-rectangular to decrease a slope of the bias field lines along agiven axis, the shape of the magnet is at least partially elliptical,the shape of the magnet is at least partially beveled, and/or the shapeof the magnetic is at least partially triangular.

In a further aspect, a sensor comprises: a first magnetic field sensingmeans comprising first and second segments wherein the first and secondsegments are located at positions of opposite magnetic field, whereinthe first and second segments are spaced from each other based uponiso-lines of the magnetic field; and a processing means for processingan output of the magnetic field sensing element. The iso-lines maycorrespond to a bias field along an axis perpendicular to a referenceaxis. The first and second segments can be dimensioned to achieve asubstantially equal bias field distribution. A length of the firstand/or second segment may be selected to equalize bias fielddistribution.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of this invention, as well as the inventionitself, may be more fully understood from the following description ofthe drawings in which:

FIG. 1 is a block diagram of a sensor having compensation for magneticfield sensing element positional misalignment in accordance with exampleembodiments of the invention;

FIG. 1A shows a schematic representation of a sensor having a bridgeconfiguration with compensation for magnetic field sensing elementpositional misalignment in accordance with example embodiments of theinvention;

FIG. 2 shows an example GMR element layer configuration that can form apart of a sensor having GMR elements in a bridge configuration withcompensation GMR element positional misalignment in accordance withexample embodiments of the invention;

FIG. 3A shows a magnet and magnetic vectors without magnetic fieldsensing element misalignment;

FIG. 3B shows a magnet and magnetic vectors with magnetic field sensingelement misalignment;

FIG. 4A shows a portion of a sensor having magnetic field sensingelements in a bridge configuration with segments at locations ofopposite bias without misalignment in accordance with illustrativeembodiments of the invention;

FIG. 4B shows an equivalent circuit for the sensor portion of FIG. 4A;

FIG. 4C shows a heat map of a magnetic field Hy (along Y axis) producedby a magnet in the plane XY;

FIG. 5 shows a portion of a sensor having magnetic field sensingelements with segments at locations of opposite bias with misalignmentin accordance with illustrative embodiments of the invention;

FIG. 6 is a flow diagram showing an example sequence of steps forproviding magnetic field sensing elements with segments at locations ofopposite bias with misalignment in accordance with illustrativeembodiments of the invention;

FIG. 7 is a schematic representation of a portion of a sensor havingmagnetic field sensing elements with segments at locations with respectto a magnet in accordance with illustrative embodiments of theinvention;

FIG. 8 is a schematic representation of a portion of a sensor havingmagnetic field sensing elements and FIG. 8A shows a circuitrepresentation of left and right bridges formed by the magnetic fieldsensing elements of FIG. 8, and FIG. 8B shows symmetric and three-pointbridges formed by the magnetic field sensing elements of FIG. 8;

FIG. 9A is a schematic representation of magnetic field sensor havingmagnetic field sensing elements and segments positioned in relation to afield of a magnet;

FIG. 9B is a schematic representation of magnetic field sensor havingmagnetic field sensing elements and segments dimensioned and/or spacedin relation to a field of a magnet;

FIG. 9C is a schematic representation of magnetic field sensor havingmagnetic field sensing elements and segments dimensioned and/or spacedin relation to a field of a magnet;

FIG. 10 is a schematic representation of bias seen by example magneticfield sensing segments;

FIG. 10A is a schematic representation of bias seen by example magneticfield sensing segments for a shaped magnet;

FIG. 11 shows example magnet shapes for magnetic field sensor;

FIG. 12 is a schematic representation of an example computer that canperform at least a portion of the processing described herein.

DETAILED DESCRIPTION

FIG. 1 is a circuit diagram illustrating an example of a magnetic fieldsensor 10 including a magnetic field sensing element 12 having biasmisalignment compensation in accordance with illustrative embodiments ofthe invention. In embodiments, the magnetic field sensing element 12 canbe positioned in relation to a magnet 13, for example. In embodiments,the magnetic field sensing element 12 senses a ferromagnetic target 14,for example, that causes changes in a magnetic field. A signalprocessing module 16 is coupled to the magnetic field sensing element 12to process the signal from the sensing element. An output module 20 iscoupled to the signal processing module 16 to provide an output signalfor a device containing the magnetic field sensor.

In one embodiment shown in FIG. 1A, the magnetic field sensing element12 of FIG. 1 comprises a GMR magnetic field sensor 110 in the form of abridge. The bridge circuit 110 includes magnetic field sensing elements,such as GMR elements 112, 114, 116, 118, disposed on the respectivebranches of the bridge 110. As shown, and described more fully below,the GMR elements 112, 114, 116, 118 can be divided into two or moresegments to provide misalignment compensation.

In the illustrative embodiment, one end of the GMR element 112 and oneend of the GMR element 116 are connected in common to a power supplyterminal V_(cc) via a node 120, one end of the GMR element 114 and oneend of the GMR element 118 are connected in common to ground via a node122. The other end of the GMR element 112 and the other end of the GMRelement 114 are connected to a node 124, and the other end of the GMRelement 116 and the other end of the GMR element 118 are connected to anode 126.

In the illustrated embodiment, node 124 of the bridge circuit 110 isconnected to a differential amplifier circuit 130. Node 126 is alsoconnected to the differential amplifier circuit 130. A first output ofthe differential amplifier circuit 130 is connected to an output module140. In embodiments, Vcc can be used to compensate for gain changes ofthe GMR elements over process and temperature. It is understood that thedifferential amplifier circuit 130 can include offset trim to correctfor GMR sensor mismatch and/or sensitivity trim to adjust gain overtemperature and process.

The magnetic field sensing planes of the GMR elements 112, 116 and 114,118 react to a magnetic field by corresponding resistances changes. GMRelements 112, 118 have maximum and minimum resistances at locationsshifted in phase to that of GMR elements 114, 116. This is due to eitherhow the magnetics of the system are configured and/or different pinningorientations of the elements. As a result, the voltages at the nodes124, 126 (mid-point voltages) of the bridge circuit 110 also change in asimilar fashion.

Magnetoresistance refers to the dependence of the electrical resistanceof a sample on the strength of external magnetic field characterized as:δ_(H)=[R(0)−R(H)]/R(0)where R(H) is the resistance of the sample in a magnetic field H, andR(0) corresponds to H=0. The term “giant magnetoresistance” indicatesthat the value δ_(H) for multilayer structures significantly exceeds theanisotropic magnetoresistance, which has a typical value within a fewpercent.

Giant magnetoresistance (GMR) is a quantum mechanical magnetoresistanceeffect observed in thin-film structures composed of alternatingferromagnetic and non-magnetic conductive layers. The effect is observedas a significant change in the electrical resistance depending onwhether the magnetization of adjacent ferromagnetic layers are in aparallel or an antiparallel alignment. The overall resistance isrelatively low for parallel alignment and relatively high forantiparallel alignment. The magnetization direction can be controlled,for example, by applying an external magnetic field. The effect is basedon the dependence of electron scattering on the spin orientation. Abridge of four identical GMR devices is insensitive to a uniformmagnetic field and is reactive when the field directions areantiparallel in the neighboring arms of the bridge.

FIG. 2 illustrates a simplified GMR sensor 200 that can form a part ofthe magnetic field sensor 10 of FIG. 1 according to an embodiment. InFIG. 2, the GMR sensor 200 includes a pinned layer 210, a metal path212, such as copper, and a free layer 214. The magnetic orientation ofthe pinned layer 210 is fixed. The magnetic orientation of the freelayer 214 is maintained in a selected alignment through anisotropy or bythe shown alternative second pinned layer 220, each of which provide apinning field, H_(an) 242 (FIG. 2b ). The magnetic orientation of thefree layer 214 rotates 242 based on the applied field.

As shown, anisotropy may be used to creates a 90° zero applied fieldorientation 240 of the free layer 220, or a 90° zero applied fieldorientation 240 may be provided with the second pinned layer 220, whichis 90° to the pinned layer.

The sensitivity of a GMR (Giant Magnetoresistance) element used in aback bias environment depends on the magnetic bias (internal or externalto the GMR structure). The bias induced by the magnet is typically notuniform and the GMR sensitivity changes with the position of the GMRwith regards to the magnet such that placement tolerances may be afactor in the accuracy of the sensor.

Embodiments of the invention provide reduction in the effect of sensingelement misalignment with respect to a magnet on GMR sensitivity bysplitting a GMR structure into at least two segments and positioning afirst GMR segment in a zone with positive bias and a second GMR segmentin a symmetric zone with opposite bias. The zones are defined by one ormore axes at least one of which may be aligned with a surface of themagnet and passing through a center of the magnet. In a configurationwithout misalignment, the first and second segments in zones of oppositebias will have the same magnitude of bias, therefore the samesensitivity. In the case of sensing element misalignment with respect tothe field, the first segment will increase/decrease its bias with aconsequent decrease/increase of sensitivity and the second segment willhave the opposite behavior with decreasing/increasing bias with aconsequent increase/decrease of sensitivity, as described more fullybelow. The first and second GMR segments attempt to compensate eachother in sensitivity in the presence of misalignment of the GMRstructure with respect to a bias magnet.

FIGS. 3A and 3B show bias variations with respect to a magnet 300.Positioning is described using x, y, and z coordinates as shown. FIG. 3Ashows a configuration with a magnetic field sensing element, which canbe provided as a GMR element, that is centered about the Y axis wherethe magnetic field sensing elements has first and second segmentssubject to opposite field polarity. The magnet 300 generates a bias onthe Y axis that is symmetric to bias on the X axis. For the purposes ofsimplicity, the zero coordinate 302 is placed at the center of themagnet 300. A point at coordinate “x1,y1” has a bias on Y axis equal andoppose to a point at coordinate “x1,−y1” so that the magnetic vector B1is equal and opposite to magnetic vector B2. As can be seen the magneticvector B1, B2 have the same length/magnitude and are located the samedistance from the x-axis. The first segment can be located at “x1,y1”and the second segment can be located at “x1,−y1.” In embodiments, thesensing element is centered with respect to the magnet.

FIG. 3B shows magnetic field sensing element misalignment along the Yaxis. The Y axis magnitude increases (in absolute value) moving from the(x,y) center of the magnet in the Y direction. Due to the misalignment,magnetic vectors B3 and B4 have the same distance between them but areoffset in the Y direction compared to magnetic vectors B1 and B2, whichcorrespond to no Y-axis misalignment. The magnetic vector B3 ispositioned further from the center of the magnet compared to B1 and hasa stronger bias on the Y axis compare to B1. The magnetic vector B4 ispositioned closer to the magnet center compared to B2 and has a weakerbias on the Y axis compared to B2. In embodiments, center is defined asthe intersection of the axis of symmetry of the magnet as shown in FIG.7. The fact that we have 0 field in the center is a consequence of thesymmetry. Also if the magnet magnetization is tilted, there is no more 0field point in the center.

It is understood that a GMR sensing element changes its resistance Rroughly proportionally to the cosine of the magnetic vector according tothis formula:R˜Hx/sqrt(Hx{circumflex over ( )}2+Hy{circumflex over ( )}2)),

where Hx is the magnetic field on the X axis, and Hy is the magneticfield on the Y aix. Hx is typically the ‘useful’ field. In theillustrated embodiment, the target moves along the X-axis (from left toright or vice-versa)

It will be this appreciated that a single GMR structure is thereforerelatively insensitive to position on the Y axis because its componenton Y axis is changing. A misalignment on the Y axis between the GMRstructure and the magnet moves the GMR magnetic vector from B1 to B3which may significantly affect the response of the GMR.

In embodiments, the GMR elements are segmented and positioned tocompensate for misalignment. For example, a first segment can bepositioned at coordinate “x1,y1” and a second segment can be positionedat coordinate “x1,−y1.” Where there is no misalignment, the first andsecond GMR segments will have substantially the same response becausethey have the same distance from X, and thus, the same Hy field.

It is understood that the Hx magnetic field has been assumed to besimilar in amplitude due to the same distance from the Y axis or due tothe use of a magnet with a uniform field in the X axis. In case ofmisalignment of the GMR structure versus the magnet in the Y direction,the two segments will both move up or down. In such a case, when thefirst segment increases its bias on the Y axis the second reduces itsbias on the Y axis to compensate for the first segment to a firstapproximation, and vice versa.

As shown above, a GMR element positioned to generate magnetic fieldvector B3 reduces its sensitivity due to the stronger field on the Yaxis, but the GMR element positioned to generate magnetic vector fieldB4 increases its sensitivity due to the weaker field on the Y axis. Thetwo sensitivities tend to compensate for the other so as to minimize theeffect of y-axis misalignment.

FIG. 4A shows an example system 400 having a GMR bridge 402 positionedwith respect to a magnet 404 without misalignment. The magnetic field inthe Z axis direction is shown by arrow 406. Note that the field in the Xdirection is not shown. A first GMR element 408 includes a first segment408 a and a second segment 408 b, a second GMR element 410 includes athird segment 410 a and a fourth segment 410 b, a third GMR element 412includes a fifth segment 412 a and a sixth segment 412 b, and a fourthGMR element 414 includes a seventh segment 414 a and an eight segment414 b.

As compared to a conventional GMR bridge, the first GMR element 408 isdivided into the first and second segments 408 a,b, each of which hassubstantially equal bias magnitude that is opposite in polarity sincethere is no y-axis misalignment. Similarly, the segments of the second,third and fourth GMR elements are subject to substantially equal bias ofopposite polarity.

In the illustrated embodiment, a voltage supply VCC can be coupled tothe first segment 408 a of the first GMR element 408 a and the fifthsegment 412 a of the third GMR element, and electrical ground GND can becoupled to the seventh segment 414 a of the fourth GMR element 414 andthe fourth segment 410 b of the second GMR element.

FIG. 4B shows an equivalent electrical circuit showing the segmentconnections to VCC and GND. It is understood that VCC and GND can becoupled to the GMR elements in a variety of configurations to meet theneeds of a particular application.

FIG. 4C shows an example heat map of the magnetic field Hy (along Yaxis) produced by an example magnet of dimension (X;Y;Z)=(5;4;3) mm inthe plane XY that is distant from the magnet by 2.5 mm. The rectangleindicates the position of the magnet in the XY plane. Units are mm for Xand Y and Oersted for the field. In the center, the map shows a gradientof Hy field along the Y axis with negative field for Y<0 and positivefield for Y>0. The Hy field is relatively constant over the X axis.

FIG. 5 shows an example system 500 having a GMR bridge 502 positionedwith respect to a magnet 504 with Y-axis sensing element/magnetmisalignment. The magnetic field in the Z axis direction is shown byarrow 506. A first GMR element 508 includes a first segment 508 a and asecond segment 508 b, a second GMR element 510 includes a third segment510 a and a fourth segment 510 b, a third GMR element 512 includes afifth segment 512 a and a sixth segment 512 b, and a fourth GMR element514 includes a seventh segment 514 a and an eight segment 514 b.

As can be seen, the distances D1, D2 from the x-axis to the firstsegment 508 a and to the second segment 508 b of the first GMR element508 are different. In embodiments, the respective segments of thesecond, third, and fourth elements are also spaced at differentdistances from the x-axis.

Since the second segment 508 b of the first GMR element 508 is closer tothe center C of the magnet than the first segment 508 a, the secondsegment has higher sensitivity to the magnetic field than the firstsegment. Where the first and second segments 508 a, b are connected inelectrical series, the total sensitivity of the first GMR elementcomprises the combined sensitivity of the first and second segments 508a,b.

In one embodiment, to a first approximation, the increased sensitivityof the second segment 508 b of the first GMR element 508 compensates forthe decreased sensitivity of the first segment 508 a due to Y directionmisalignment since δR=δHx/sqrt(Hx0²+Hy²) where δR is the amplitude ofthe signal, δHx is the variation of the field along X axis that generatethe signal; Hx0 is the static field along X and Hy is the static fieldalong Y. When Hy increases signal decreases, when Hy decreases, signalincreases.

FIG. 6 shows an example sequence of steps for providing misalignmentcompensation in accordance with example embodiments. The steps of FIG. 6can be understood in conjunction with the example embodiment of FIG. 5.In step 600, segments of a first magnetic field sensing element arepositioned at locations of opposite field bias provided by a magnet. Inembodiments, magnetic field sensing elements are configured in a bridge.In embodiments, the magnetic field sensing elements comprise GMRelements.

In step 602, segments of a second magnetic field sensing element arepositioned at locations of opposite field bias. In step 604, segments ofa third magnetic field sensing element are positioned at locations ofopposite field bias. In step 606, segments of a fourth magnetic fieldsensing element are positioned at locations of opposite field biasprovided by a magnet. As described above, segments of a magnetic fieldsensing element at locations of opposite bias compensate for positionalmisalignment of the elements with respect to a magnetic field, which canbe provided by a bias magnet.

While example embodiments are shown and described in conjunction withGMR elements, it is understood that other types of MR elements can beused, such as TMR elements.

FIG. 7 shows an example embodiment of a back bias ‘speed’ sensor havingfirst and second bridges with three groups of GMR elements (left,center, right) with the GMR elements placed in relation to a magnet forremoving sensitivity to the common mode field and alignment bias. TheGMR elements are subject to opposite bias. The sensor provides speed anddirection information of a target with first and second bridges havingGMR elements located in different X positions, as shown. Due to thesymmetry of the sensor, when the die and the magnet are perfectlyaligned, a symmetric bridge has the GMR elements subject to same bias.Therefore, the sensor is immune to stray fields when the die and magnetare perfectly aligned.

FIG. 8 shows a sensor having GMR elements and FIGS. 8A and 8B showalternative bridge constructions in which GMR elements are subject toopposite bias. FIG. 8 shows first and second GMR bridges each havingfour elements where each element has first and second segments. FIG. 8Ashows the left bridge and right bridge for bridges in the sensor of FIG.8. Output signals in the left and right bridges can be used to determinespeed and direction information. In one embodiment, subtraction and sumof signals in the left and right bridges outputs speed and directioninformation. The GMR elements are labeled such that subscription 1refers to left, r refers to right, and c refers to center. Looking toFIG. 8, yokes Ax and Cx may be referred to a outer yoke Bx may bereferred to as central or inner yokes. From left to right in FIG. 8, theGMR elements are listed as A_(l), A_(c), B_(l), B_(cl), B_(cr), B_(r),C_(c), C_(r). As seen in the left bridge of FIG. 8A, GMR element A_(l)includes first and second segments A_(la), A_(lb), the GMR elementB_(cl) includes third and fourth elements B_(cla), B_(c1b), and so on.

In this arrangement, the segments of the GMR elements do not experiencethe exact same bias conditions. For example, the bias field, which canbe generated by a magnet, along Z axis (FIG. 8) varies slightly betweeninner and outer yoke. This produces a difference in sensitivity of theelements, resulting in a global sensitivity to common mode field.

FIG. 8B shows symmetric and three point bridge configurations that maybe useful for a back bias speed sensor. In an embodiment, the symmetricbridge of A_(l), C_(c), C_(r), and A_(c), can be referred to as adirection channel and the three point bridge can be referred to as aspeed channel. Yokes A_(x) and C_(x) can be referred to as outer yokesand yokes B_(x) can be referred to as central or inner yokes (see FIG.8).

In embodiments, yokes should be placed by pairs in a symmetric mannerrespective to the magnet. One yoke should be placed at a position +Ypand the second Ym=−Yp (assuming Y=0 is at the center of the magnet).Then the spacing S (e.g., 2*Yp) is selected high enough so that the biasdue to the magnet is large enough to ensure a proper compensation of themisplacement along Y axis and stray field along that same axis and smallenough to ensure the sensitivity is not too diminished for a far air gapsignal. In embodiments, there is compensation for bias of the GMR andgood tolerance to misplacements over airgap.

As shown in FIGS. 9A and 9B, to promote substantially equal bias on theGMR elements, the GMR elements and segments can be dimensioned and/orspaced according to the iso-lines of bias field along the axisperpendicular to the reference direction, i.e. HyHy. As can be seen, inthe example embodiment, there is a left GMR element, a center GMRelement and a right GMR element, each having first and second segments.The left and right GMR elements are subject to different bias fieldsthan the center elements as indicated by the iso-lines. The distancebetween the first and second segments of the left GMR element is ε_(c)and the length of the segment is δ_(l). The distance between thesegments of the center GMR element is ε_(c) and the length of thesegment is δ_(c). The distance between the first and second segments ofthe right GMR element is ε_(r) and the length of the segment is or. Inthe illustrated embodiment of FIG. 9A, δ_(l)=δ_(r)=δ_(c) andε_(l)=ε_(r)=ε_(c). In the illustrated embodiment of FIG. 9B,δ_(l)=δ_(r)≠δ_(c) and ε_(l)=ε_(r)≠ε_(c), as the center segment spacingand dimensions are different than the left and right segment spacing anddimension. In embodiments, δ_(c) is chosen so that HyHy at the bottom ofthe upper yokes is the same on all left, center and right yokes. AndHyHy at the top of the upper yokes is the same on all left, center andright yokes. In embodiments, the yokes are all the same size and onlythe vertical spacing changes. The spacing is chosen so that the averageHyHy value across the central yoke is the same as on the sides. FIG. 9Cshows identical average bias on the elements.

It is understood that the length of the segments and distance betweensegments can be unique and can be configured to meet the needs of aparticular application.

The arrangement of FIG. 9B, for example, distributes substantially equalbias through the GMR bridge elements. To keep the same sensitivity,central yokes and outer yokes should have the same resistance in absenceof any magnetic field. As the square resistance of the stack forming theGMR elements is the same and the vertical length is fixed, zero fieldresistance can be adapted by adapting the GMR element width and/oradding a GMR segment placed right beside an existing element. Suchelements can be connected either in series or in parallel with existingelements. To this end, the sensitivity in Ω/Oe can be made substantiallyequal between each GMR element (when both the die and the magnet areperfectly aligned).

In another aspect, a bias magnet can be shaped to decrease thesensitivity to the common mode field over X axis misplacement of thesensor elements. As shown in FIG. 10, for a rectangular magnet crosssection, bias HyHy can vary significantly when misplacement in the Xaxis occurs, as shown. Thus, due to sensor element misplacement, thesensor starts to be sensitive to stray field. The bias Hy is shown forthe upper segment of the left element, the upper segment of the centerelement, and the upper segment of the right element for the embodimentof FIG. 9B in which the center element segments are spaced anddimensioned differently than the left and right element segments.

As shown in FIG. 10A, by changing the cross section of the magnet in theXY plane from square to, for example, a bevel perimeter shown in FIG.11, the slope of the bias Hx at which the GMR elements are located canbe decreased, and may approach zero. When X-axis misplacement occurs,the bias does not change significantly. Therefore, sensitivity to strayfield does not vary significantly through a range of X misplacement. Inan ideal position, one is in the center and as soon as there ismisalignment on X the 3 moves in such direction but because the profileis flat (slope is null) they still work as we are in the middle. Thus,there is good immunity to misalignment because there is no change. Inembodiments, Hy depends on the distance to the top/bottom edge of themagnet. The closer to the edge, the higher Hy is. By reducing the heightof the magnet on the sides we get these top and bottom edges closer tothe yokes so that Hy increases again. That is how the function changesfrom something going down to 0 to something increasing again.

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can comprise, but is notlimited to, a Hall Effect element, a magnetoresistance element, and/or amagnetotransistor. As is known, there are different types of Hall Effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, for example, a spinvalve, an anisotropic magnetoresistance element (AMR), a tunnelingmagnetoresistance (TMR) element, a magnetic tunnel junction (MTJ), and aspin-valve. The magnetic field sensing element may be a single elementor, alternatively, may include two or more magnetic field sensingelements arranged in various configurations, e.g., a half bridge or fullbridge. Depending on the device type and other application requirements,the magnetic field sensing element may be a device made of a type IVsemiconductor material such as Silicon (Si) or Germanium (Ge), or a typeIII-V semiconductor material like Gallium-Arsenide (GaAs) or an Indiumcompound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elementstend to have an axis of maximum sensitivity parallel to a substrate thatsupports the magnetic field sensing element, and others of theabove-described magnetic field sensing elements tend to have an axis ofmaximum sensitivity perpendicular to a substrate that supports themagnetic field sensing element. In particular, planar Hall elements tendto have axes of sensitivity perpendicular to a substrate, while metalbased or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) andvertical Hall elements tend to have axes of sensitivity parallel to asubstrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back-biased or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

FIG. 12 shows an exemplary computer 1200 that can perform at least partof the processing described herein. The computer 1200 includes aprocessor 1202, a volatile memory 1204, a non-volatile memory 1206(e.g., hard disk), an output device 1207 and a graphical user interface(GUI) 1208 (e.g., a mouse, a keyboard, a display, for example). Thenon-volatile memory 1206 stores computer instructions 1212, an operatingsystem 1216 and data 1218. In one example, the computer instructions1212 are executed by the processor 1202 out of volatile memory 1204. Inone embodiment, an article 1220 comprises non-transitorycomputer-readable instructions.

Processing may be implemented in hardware, software, or a combination ofthe two. Processing may be implemented in computer programs executed onprogrammable computers/machines that each includes a processor, astorage medium or other article of manufacture that is readable by theprocessor (including volatile and non-volatile memory and/or storageelements), at least one input device, and one or more output devices.Program code may be applied to data entered using an input device toperform processing and to generate output information.

The system can perform processing, at least in part, via a computerprogram product, (e.g., in a machine-readable storage device), forexecution by, or to control the operation of, data processing apparatus(e.g., a programmable processor, a computer, or multiple computers).Each such program may be implemented in a high level procedural orobject-oriented programming language to communicate with a computersystem. However, the programs may be implemented in assembly or machinelanguage. The language may be a compiled or an interpreted language andit may be deployed in any form, including as a stand-alone program or asa module, component, subroutine, or other unit suitable for use in acomputing environment. A computer program may be deployed to be executedon one computer or on multiple computers at one site or distributedacross multiple sites and interconnected by a communication network. Acomputer program may be stored on a storage medium or device (e.g.,CD-ROM, hard disk, or magnetic diskette) that is readable by a generalor special purpose programmable computer for configuring and operatingthe computer when the storage medium or device is read by the computer.Processing may also be implemented as a machine-readable storage medium,configured with a computer program, where upon execution, instructionsin the computer program cause the computer to operate.

Processing may be performed by one or more programmable processorsexecuting one or more computer programs to perform the functions of thesystem. All or part of the system may be implemented as, special purposelogic circuitry (e.g., an FPGA (field programmable gate array) and/or anASIC (application-specific integrated circuit)).

Having described exemplary embodiments of the invention, it will nowbecome apparent to one of ordinary skill in the art that otherembodiments incorporating their concepts may also be used. Theembodiments contained herein should not be limited to disclosedembodiments but rather should be limited only by the spirit and scope ofthe appended claims. All publications and references cited herein areexpressly incorporated herein by reference in their entirety.

Elements of different embodiments described herein may be combined toform other embodiments not specifically set forth above. Variouselements, which are described in the context of a single embodiment, mayalso be provided separately or in any suitable subcombination. Otherembodiments not specifically described herein are also within the scopeof the following claims.

What is claimed is:
 1. A sensor, comprising: a magnet to provide amagnetic bias field; a bridge comprising at least first, second, third,and fourth magnetic field sensing elements, wherein the first magneticfield sensing element comprises first and second segments, wherein thefirst and second segments are located at positions of opposite bias ofthe magnetic bias field, wherein the first and second segments arespaced from each other based upon iso-lines of the magnetic bias field,and wherein the iso-lines of the magnetic bias field align with an axisperpendicular to a reference axis; and a processing module configured toprocess a signal from the magnetic field sensing element.
 2. The sensoraccording to claim 1, wherein the first and second segments aredimensioned to achieve a substantially equal field distribution of themagnetic bias field.
 3. The sensor according to claim 1, wherein alength of the first and/or second segment is selected to equalizedistribution of the magnetic bias field.
 4. The sensor according toclaim 1, wherein the length and spacing of the first and second segmentsis selected to achieve a given zero field resistance.
 5. The sensoraccording to claim 1, wherein the second magnetic field sensing elementcomprises third and fourth segments located at positions to generatemagnetic field bias in opposite directions for reducing sensitivity dueto misalignment of the third and fourth segments.
 6. The sensoraccording to claim 5, wherein the first and second magnetic fieldsensing elements are configured in half-bridge configuration.
 7. Thesensor according to claim 1, wherein the third magnetic field sensingelement comprises fifth and sixth segments and the fourth magnetic fieldsensing element comprises seventh and eighth segments.
 8. The sensorsystem according to claim 1, wherein the first magnetic field sensingelement comprises GMR elements.
 9. The sensor system according to claim1, wherein the first magnetic field sensing element comprises TMRelements.
 10. The sensor according to claim 1, wherein a shape of themagnet providing the magnetic bias field is non-rectangular to decreasea slope of the bias field lines along a given axis.
 11. The sensoraccording to claim 10, wherein the shape of the magnet is at leastpartially elliptical.
 12. The sensor according to claim 10, wherein theshape of the magnet is at least partially beveled.
 13. The sensoraccording to claim 10, wherein the shape of the magnetic is at leastpartially triangular.
 14. A method, comprising: employing a magnet toprovide a magnetic bias field; employing a bridge comprising at leastfirst, second, third, and fourth magnetic field sensing elements,wherein the first magnetic field sensing element comprises first andsecond segments wherein the first and second segments are located atpositions of opposite bias of the magnetic bias field, wherein the firstand second segments are spaced from each other based upon iso-lines ofthe magnetic bias field, and wherein the iso-lines of the magnetic biasfield align with an axis perpendicular to a reference axis; andemploying a processing module configured to process a signal from themagnetic field sensing element.
 15. The method according to claim 14,wherein the first and second segments are dimensioned to achieve asubstantially equal distribution of the magnetic bias field.
 16. Themethod according to claim 14, wherein a length of the first and/orsecond segment is selected to equalize distribution of the magnetic biasfield.
 17. The method according to claim 14, wherein the length andspacing of the first and second segments is selected to achieve a givenzero field resistance.
 18. The method according to claim 14, furthercomprising employing a second magnetic field sensing element havingthird and fourth segments located at positions to generate magneticfield bias in opposite directions for reducing sensitivity due tomisalignment of the third and fourth segments.
 19. The method accordingto claim 18, wherein the first and second magnetic field sensingelements are configured in half-bridge configuration.
 20. The methodaccording to claim 14, wherein the third magnetic field sensing elementcomprises fifth and sixth segments and the fourth magnetic field sensingelement comprises seventh and eighth segments.
 21. The method accordingto claim 14, wherein the first magnetic field sensing element comprisesGMR elements.
 22. The method according to claim 14, wherein the firstmagnetic field sensing element comprises TMR elements.
 23. The methodaccording to claim 14, wherein a shape of the magnet providing themagnetic bias field is non-rectangular to decrease a slope of the biasfield lines along a given axis.
 24. The method according to claim 23,wherein the shape of the magnet is at least partially elliptical. 25.The method according to claim 23, wherein the shape of the magnet is atleast partially beveled.
 26. The method according to claim 23, whereinthe shape of the magnetic is at least partially triangular.
 27. Asensor, comprising: a first magnetic field sensing means comprisingfirst and second segments wherein the first and second segments arelocated at positions of opposite magnetic field bias generated by amagnet, wherein the first and second segments are spaced from each otherbased upon iso-lines of the magnetic field; and a processing means forprocessing an output of the magnetic field sensing element.
 28. Thesensor according to claim 27, wherein the iso-lines correspond to a biasfield along an axis perpendicular to a reference axis.
 29. The sensoraccording to claim 27, wherein the first and second segments aredimensioned to achieve a substantially equal bias field distribution.30. The sensor according to claim 27, wherein a length of the firstand/or second segment is selected to equalize bias field distribution.